Compressed-Air Discharge-Pressure Setpoint Savings
Prices the cheapest compressed-air conservation measure there is: turning the discharge pressure down. Because compression power rises with the pressure ratio, the isentropic power ratio between two setpoints gives the exact percent saved - which reproduces the DOE rule of about half a percent of compressor energy per psi. Dropping 120 to 105 psig on a 50 kW compressor saves ~7 percent, roughly $2,000 a year, for turning a knob. The reduced setpoint must still hold the minimum tool pressure after system drop, which is why fixing leaks and piping is what unlocks it. An energy-savings estimate, not a metered result.
Formula and source
work_current = ((current_psig + 14.7) / inlet_psia)^((k-1)/k) - 1; work_reduced = ((reduced_psig + 14.7) / inlet_psia)^((k-1)/k) - 1; pct_saved = 1 - work_reduced / work_current; kw_saved = input_kw x pct_saved; annual_kwh = kw_saved x run_hours; annual_savings = annual_kwh x rate_kwh. (k = 1.4)
The isentropic compression-power ratio (percent saved = 1 - [(P_reduced/P1)^((k-1)/k) - 1] / [(P_current/P1)^((k-1)/k) - 1]), which reproduces the DOE rule of roughly 0.5% of compressor energy per psi of reduction, by name; k = 1.4 for air is a named constant.
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